As shown diagrammatically in accompanying FIG. 1, textured filter paper is generally prepared by means of a conventional method that consists in using a machine 10 to prepare a non-woven structure 12 in conventional manner, the structure 12 comprising two superposed layers, namely a layer based on synthetic fibers and a layer of cellulose fibers, after which:
a) a series of fluid jets 20 are applied to the non-woven structure 12 to texture the paper in a selected pattern; and then
b) the textured non-woven structure is subjected to a heating operation in order to fix the synthetic fibers.
The fluid jet texturing operation is generally performed by spraying jets of fluid 20 onto the paper 12 through a rotary cylinder 22 having openings or through a moving strip likewise having openings (not shown). During this operation, the paper 12 must naturally be supported by support means which are omitted from FIG. 1 to simplify the illustration. The fluid used is generally water. This fluid jet texturing technique is well known to the person skilled in the art and has given rise to abundant literature.
The hot fixing operation is generally performed by passing the textured paper over a rotary cylinder 30 provided with heater means. For example, the cylinder 30 may be heated to a temperature of about 200.degree. C. It may optionally be of the "through air" type designed to blow hot air through the sheet. It may also be replaced by a hot air tunnel oven.
An object of the present invention is to propose a novel method of preparing paper for filter bags, which method makes it possible to improve the properties of the product obtained.